Q: So before we get into a discussion about your book, Time: A Philosophical Introduction, tell me about what got you interested in philosophy?
A: In one sense the answer goes so far back that I don’t even know how to answer that question. My dad was a great books major with an interest in philosophy, so I grew up with a family who had philosophy books on the shelves. It was a very intellectual Catholic environment, so it means philosophy was very central even in our dinner table conversations.
Professionally, though, I always thought I was going to be a physicist. . I was a science fiction reader from very early on. Ultimately I wanted to understand the world. To me that’s what ties together everything I’ve ever been interested in: how things worked. And through high school and much of college, physics seemed like the best bet for that. But I wasn’t quite good enough at math to do the kind of high level physics that I wanted to do. I could follow it, but I wasn’t quite good enough to add to it. In my year I graduated in a class of 5, and I am the only one without a Ph.D. in either physics or engineering.
But more than that, as an undergrad I was also in the Program of Liberal Studies, Notre Dame’s great books program. And what I loved about philosophy was that it allowed me to play in this much bigger sandbox. I mean, what other academic discipline can I do relativity theory in the morning and Plato’s Symposium in the afternoon?
Q: So what got you interested specifically in questions about time?
A: I really started with a very particular question about time. I knew from what I’d read that the twin paradox was not really a paradox, but that that wasn’t quite the end of the story. The twin paradox is the idea Einstein raises in the very first relativity paper. In its classical form, you have two identical twins, one on a rocketship traveling some significant fraction of the speed of light, while the other is on earth. The rocketship does a round trip and comes back to earth, and the twins don’t agree on how long the trip takes. The trip takes longer for the trip on earth than it does for the one on the rocket. And while you can do the math showing this to be true, it still seems counter to our common sense of how time seems to behave for us. I think it reveals a deeper puzzle that we don’t actually know how to fit our common sense notion of time in with this picture of time from science.
Now at the time people like philosopher Henri Bergson thought that the counterintuitive nature of Einstein’s theories this just showed that relativity theory was confused and not a theory of time. Now it’s generally thought that Bergson lost that debate with Einstein, to disastrous effects to his reputation as a philosopher. This episode exemplifies what I call Simplicius effect, after the Aristotelian figure in Galileo’s dialogue: when philosophers get in fights with physicists over physics, bad things happen to philosophers. To try to argue that the physics is bad because it doesn’t make philosophical sense has just been a losing argument, historically speaking.
But thinking more generally about relativity, though, what interested me here was that if we really understood the implications of the idea that there is no determinate quantity of time between events—that the quantity depends on the path between them—then this would radically alter our view of time.
Q: So this brings us to your book Time: A Philosophical Introduction. Can you give us a sketch of how you see the debates you discuss in the book?
A: The organizing theme of the book is being versus becoming, starting with the ancient argument between Parmenides and Heraclitus, and then Plato as the middle ground between them. But over the last 50 years several different questions of time have collapsed into a single question of time, whether time is metaphysically fundamental. For example, take the question of the existence of the past and future. There’s one position, presentism, that in its classical form holds that that which exists now, in the present, is the only sort of thing that exists at all. So the past and the future don’t exist in quite the same way that the present does. On the other side, you have eternalism or block universe theories, which hold that past, present, and future, all have the same ontological status. The former position is usually called A-theory, the latter called B-theory, following J.M.E McTaggart’s usage.
In a famous paper in Mind called “The Unreality of Time” McTaggart argued that time isn’t real because it’s self-contradictory. He begins by noticing that we have two different ways of “ordering” the moments of time. On one ordering, which he calls the A-series, we order moments according to their distance into the past or the future from the present. The B-series simply orders them by earlier or later. McTaggart’s actual argument is dense, and probably incoherent, but he claims that the A-series is self-contradictory. He seems to see “presentness” and “pastness” as incompatible properties that moments, or events, can possess. That is, the same thing cannot be both past and present, obviously. However, past events are past now. In order for them to have the property of “pastness” now they must be present, in some sense. Therefore he concludes that every moment or event always possesses both properties, contrary to the definition of the properties. The whole things a bit of a mess—I try to unpack a lot of the messiness in Chapter 3—but I think a lot of people miss that McTaggart is making a claim about temporal passage, not ontology.
Q: You say he isn’t talking about ontology, but his article is titled “The Unreality of Time,” which does suggest that a question of ontology and reality is pretty central issue for him. Why do you think this title is misleading?
A: It’s misleading because McTaggart isn’t interested in whether the contents of various times are real or not. McTaggart wants to claim that reality isn’t arranged in time at all; time is purely ideal. I don’t talk about it in the book, but I think one of the problems with the way people treat McTaggart on time is that his arguments regarding time tends to get isolated from the fact that he’s a full-blown Hegelian absolute idealist. His actual ontology is simply bizarre to say the least.
One of the things I try to show in the book is how there are several different questions about time that are related but ultimately independent of each other. Many people follow C.D. Broad who says the only way to believe in temporal passage coherently is to subscribe to the ontological claim that things come into existence and, maybe, out of existence. Relativity theory–especially something called Stein’s Theorem–gives us really strong reasons to be an ontological eternalist. But many philosophers want to go right from these kinds of claims to the idea that time doesn’t pass at all, i.e. the block universe. That’s what I want to resist.
The problem is that both sides want to immediately go from the ontological question to the question of whether time is an illusion. I want to resist that inference; these are logically distinct questions.. I want us to be aware of the plurality and independence of these questions.
I guess it ultimately comes down to the distinction Wilfrid Sellars described between the manifest and scientific images. There are good reasons from a scientific perspective to think that there is no passage of time, but in the manifest image of how we experience the world time is fundamental. Indeed a world without time is hard to imagine. And I want to say that these positions are working at cross-purposes, addressing different kinds of problems.
Q: How would you respond to the objection that we need some sort of resolution between the competing conceptions? Or are you just willing to that these are two irreducible facets of reality?
A: So, I think time is a natural phenomenon, in that it gets its traction from the perspective of what the Scholastics called a philosophy of nature and Aristotle called physics, namely what the world looks like on the inside. This kind of philosophy is neither science nor metaphysics, strictly speaking. I think this perspective of a philosophy of nature is really missing from contemporary Anglo-American philosophy, largely because of the impoverished taxonomy of what counts as philosophy. We might say that philosophy of nature studies things that are fundamental for us as occupants of a particular kind of material world, but are not necessarily fundamental to the nature of existence itself that would make them belong to metaphysics proper.
On this view, from the inside view of the world time seems to pass. But it shouldn’t be surprising that if we try to describe the world sub specie eternitas, we find eternity. To describe the world in the language of mathematical physics is to see the world in eternity. And these are both true. I think we can tell a story why there is a world where in a certain sense there really is a four-dimensional space-time manifold—i.e. with no passage of time—but yet it still looks this other way to those of us who live on the inside of it. This account isn’t psychological or idealistic, but physical: it’s not just a four-dimensional manifold, but one with a particular structure given by the Lorenz metric, which makes a clear distinction between temporal and spatial dimensions. Time only passes along the world-lines of entities within space-time. For long, thin beings like us, that’s just the way the world would appear.
Q: You’ve been using the concept of nature a lot. Do you have a specific conception of what you take a “natural” entity to be?
A: Peter Hylton was at UIC when I was a grad student. Hylton was developing a conception of naturalism, following Quine, that I find very attractive. This kind of naturalism is a big tent notion of naturalism, where the natural world is the world as it presents itself to us, both in common sense and in experiments, theorizing, etc. I go back in forth on this: take a question like whether David Chalmers of The Conscious Mind a naturalist. There is some way of construing naturalist such that the answer is “Yes,” but that’s going to look a whole lot different from what often goes by “naturalism.” To me the attractive feature of naturalism is that they serve usefully as a replacement for the benefits that the Logical Empiricists got from verificationism. Carnap was trying to capture that our philosophical theorizing needs to be disciplined by the world. Does this philosophical theory provide a useful understanding of some phenomena? Ultimately there is some kind of pragmatism at base here, which of course is very much there in Quine’s work as well.
Q: Is there something that surprised you or something you changed your mind on while working on this?
A: One thing that I am convinced is more of a problem than I used to think is accommodating agency within eternalism. Students were actually the ones who convinced me of this: being responsible for an event can’t just be that we bear a particular causal connection to it, but rather that one is the entity that brought it into existence. That’s what we hold people responsible for (for good or ill). If it was already there to begin with, then it’s difficult to see how I’m responsible for it. I’m not convinced there’s a solvable problem. I used to think that a kind of compatibilism was the right answer, but I’m more convinced that there’s a missing piece to that account. I just don’t know what that missing piece is.
That students showed me this is what I find valuable about teaching undergraduates: they don’t come to these problems with sophisticated accounts, but rather with very straightforward approaches. That perspective can be useful in a lot of ways.
Q: So, as you said, you find something attractive about some kind of continuity between philosophy and science. How do you see the relationship between science and philosophy?
A: I see what I’m doing as scientific theorizing at a very high level of abstraction. If theoretical physicists are researchers who build models of experimental phenomena, then I see what I’m doing is treating the outputs theoretical physics as data for building a model of the world. I really don’t think there is anything that can be distinctly called philosophical knowledge. Just to give one example, relativity theory pretty much blows up our understanding of space and time. And philosophy of time in particular that isn’t in contact with the science just seems like wheel-spinning to me; whatever it is that they’re generating theories of doesn’t seem real.
Q: So it’s interesting you claim that there’s no distinct philosophical kind of knowledge. The more eliminativist brands of naturalism would probably agree with that and conclude that philosophers should just be doing science, and that there’s no need to have a distinctive philosophy department separate from the other departments in the academy. Do you agree with this? Is there something philosophy brings to the table that other departments wouldn’t necessarily provide?
A: I think what philosophy provides is a connection to broader conceptual frameworks. As I mentioned earlier, it creates a situation where you can make connections between, say, relativity theory and Plato. Philosophy is where you engage with valuable ideas that help us engage with active problems that probably would otherwise not be read or taught. Having a place where people can come learn from those kinds of sources is valuable, even for science. Einstein was engaged with much of the philosophical tradition. He read Schopenhauer as a child, he was deeply influenced by Spinoza. It’s now clear that the verificationist kinds of arguments you see in Einstein from 1905-1915 are anchored in careful readings of Hume’s Treatise, of Mach, and plenty of others.
If I were reasonably confident that people would learn those things elsewhere in other departments, that physicists were still being educated on big picture stuff in philosophical terms, then I would be happier with the diffusion of the philosophy department. But for legitimate reasons that doesn’t happen. The technical knowledge necessary for getting people up to speed in physics is enormous. I tell my philosophy of science class—most of whom are science majors—that what they’re learning in science classes is not to help them understand science as such, but to get them as quickly up to speed so that they can be trusted to make meaningful contributions at the frontiers of science.
Q: An additional worry here might be the division of labor argument, what’s sometimes called the problem of dual expertise: it’s really difficult to train people to be sensitive to the philosophical aspects while simultaneously getting them up to speed on, say, the physics. It’s hard to get people who can do both of those things well.
A: Right, and for me, I think of philosophy departments as the place where people who are doing interesting, valuable work, but don’t have natural homes elsewhere in the academy.
Q: I think it’s Michael Friedman who suggested in his lectures in Dynamics of Reason that the value of philosophy is that it provides a source of ideas and possibilities that scientists can turn to when their current paradigm is inadequate to solve a given problem. Would you agree with this kind of position?
A: Yeah, Michael was my original dissertation advisor at UIC until he left to go to Indiana University-Bloomington. He stayed on my committee even after he left, though. I think his neo-Kantian direction was one of two major influences on me, the other being, as I mentioned earlier, the kind of naturalism exemplified by Peter Hylton and Bill Hart. So, yes, I think that sounds pretty close to my position.
Q: Very interesting. So we’ve mentioned several instances in the history of science that are very influential on our understanding of philosophy. More abstractly, what sort of value do you find in studying—and teaching—the history of science.
A: I think it does a couple things. First, as all history does for me, it creates a real sensitivity to contingency: that we took this path rather than some other way, for reasons that don’t seem to have any clear explanation. That sense of contingency is important for itself, but, second, sometimes these paths not taken often have valuable stuff in them that’s worth mining. For example, I’ve been looking at how Leibniz’s monadological metaphysics can be useful to make sense of field-based ontology. Monads have two interesting features. One is the property of occupying space but without volume, so that in any finite volume there are an infinite number of monads. But the other interesting feature is that the state of a given monad depends on the state of the other monads in the universe without causally depending on them. So think about an electric field at a given location in space; the value of the field at that location is precisely what it is because that is the only value that is consistent with all the other values in the universe. So there is a kind of holism at work in Leibniz’s work where the value of the field is something representing to itself the value of everything else into the world. He’s really trying to make sense of continuity that doesn’t collapse into monism. It might be useful to apply that Leibnizian language to the behavior of fields.
Q: You’re an avid reader of science fiction. How does science fiction help you think through philosophical issues?
A: At its best, it forces us to consider things as possible that philosophers like to say are not. We philosophers insist that the world can’t work this way, then someone writes a story that forces us to think carefully on these issues. The classic case of this is Joe Haldeman’s The Forever War. The whole structure of the novel is based on the time dilation of the twin paradox, where a soldier in the first interstellar war gets left further and further behind by the culture he’s ostensibly defending because he’s flying to worlds at close to the speed of light, so he doesn’t age. Now while the novel is in one sense about Haldeman’s return from the Vietnam War, it’s also a meditation on relativity theory.
Q: Finally, what are some sources you would recommend for people interested in this subject area?
A: If you’re interested in the physics, it’s a bit dated now, but it’s hard to beat Hawking’s Brief History of Time. A more updated account would be Kip Thorne’s Black Holes and Time Warps. From the science fiction element, Thorne was an executive producer for the movie Interstellar. By the way, all of the space-time physics in that movie is pretty much perfect. In fact, designing the scene approaching the mouth of the wormhole for that movie actually generated two published papers for Kip Thorne: one on the mathematics of what a mouth of a wormhole would look like, and another on the computer coding required to generate that visual.
On the philosophical side of things, even though he’s a physicist Paul Davies’ About Time: Einstein’s Unfinished Revolution helps bridge the gap between the science and the philosophy. I also highly recommend Barry Dainton’s work Time and Space.